1. Field of the Invention
The present invention relates to a boundary detector and a boundary detecting method that acquire image information based on an image supplied from a camera that is mounted on a vehicle and picks up an image of a road surface, and detect a boundary drawn on the road surface based on the acquired image information.
2. Description of the Related Art
In recent years, an apparatus has been developed for picking up an image of a road surface in front of a vehicle with a camera, detecting a boundary, i.e., a white line, drawn on the road surface based on the image picked up by the camera, and automatically driving the vehicle on a lane delineated by the white line. For the realization of automatic driving, the lane must be properly detected, in other words, a detector is required for processing the image picked up by the camera to detect the lane, i.e., the white lines. Such detectors are disclosed in Japanese Patent Applications Laid-Open Nos. H08-320997, and 2001-014595, for example.
A vehicle lane detector disclosed in Japanese Patent Application Laid-Open No. H08-320997, measures a maximum value of edge point counts of an edge component that represents a straight line component, based on image information on the right and the left sides of the vehicle and immediately in front of the vehicle. The vehicle lane detector, based on the measured maximum value, recognizes that the image belongs to a dotted lane marker when the maximum value changes periodically, and that the image belongs to a solid lane marker when the maximum value remains constant. Thus, the vehicle lane detector recognizes the lane of the vehicle based on the results of recognition of the right and the left lane markers.
Another vehicle lane detector disclosed in Japanese Patent Application Laid-Open No. 2001-014595, detects white line candidate points through processing of an image captured by a video camera attached to a front part of a vehicle. The vehicle lane detector selects only the white line candidate points that are determined to be a part of a white line among all the white line candidate points, to calculate a detection ratio, and determines a type of the white line based on the detection ratio.
On a bypass highway, for example, a plurality of main lanes is provided together with additional lanes such as a lane for right turn or a lane for left turn to allow a vehicle to turn right or left at an intersection ahead of the vehicle. With the lanes for right turn and left turn, an overall road width widens and white lines that mark the lanes are drawn so as to bend from the white line of the main lane to outward. When there is a right turn lane added to the main lane on which a vehicle runs, for example, a white line detector may mistakenly detects the white line of the right turn lane as the white line of the main lane. The white line detector is required to correctly determine whether the detected white line belongs to the main lane or to the right turn lane. Above described two patent applications do not particularly disclose techniques to prevent such inconvenience and therefore are not immune to detection error of the white lines delineating the lanes.